Abrasive Tool and a Method for Finishing Complex Shapes in Workpieces

ABSTRACT

An abrasive tool includes a bonded abrasive body having abrasive grains contained within a bonding material, wherein the bonded abrasive body comprises a complex shape having a form depth (FD) of at least about 0.3. The form depth is described by the equation [(R1−Rs)/R1], wherein Rs is a smallest radius (Rs) at a point along the longitudinal axis of the bonded abrasive body and R1 is a largest radius (R1) at a point along the longitudinal axis of the bonded abrasive body. The abrasive tool can be used to finish complex shapes in workpieces.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §120 to and is adivisional of U.S. application Ser. No. 13/198,916 entitled “AbrasiveTool and a Method For Finishing Complex Shapes in Workpieces,” by Besseet al., filed Aug. 5, 2011, which in turn claims priority under 35U.S.C. §119(e) to U.S. Patent Application No. 61/371,581 entitled“Abrasive Tool and a Method For Finishing Complex Shapes in Workpieces,”by Besse et al., filed Aug. 6, 2010, both of which are assigned to thecurrent assignee hereof and incorporated herein by reference in theirentireties.

BACKGROUND

1. Field of the Disclosure

The following is directed to abrasive tools and methods of finishingcomplex shapes in workpieces using such abrasive tools, and moreparticularly, use of bonded abrasive tools having particular shapes forfinishing of complex shapes within workpieces.

2. Description of the Related Art

Within the industry of finishing, various processes may be employed tofinish workpieces. However, in the particular context of finishingworkpieces to have complex shapes, few options are available since suchfinishing operations require exacting surface contours and tightdimensional tolerances. Certain preferred approaches are milling orbroaching, where blades are used to cut the complex shape in theworkpiece. However, broaching can be an expensive operation, due to hightooling costs, expensive machinery, set-up costs, tooling regrindingcosts and slow material removal rates. Milling processes are generallyvery slow, especially in machining difficult-to-machine materials, suchas nickel alloys.

Still, in the context of forming retention slots in turbine disks, whichare used to hold or retain turbine blades around the periphery of thedisk, broaching is the preferred approach throughout most of theindustry. Current practice in the aerospace industry is to machine slotsinto the disk by use of a broaching machine, which is a linear cuttingmachine that drives successively larger cutters through the disk slot,with the final cutters having a desired complex shape (i.e., are-entrant shape) of the finished slot. Broaching is illustrated in U.S.Pat. No. 5,430,936 to Yadzik, Jr. et al.

Another method for producing profiled parts is illustrated in U.S. Pat.No. 5,330,326 to Kuehne et al. The method involves pre-shaping andfinish grinding a blank in one chucking position with at least oneprofiled grinding wheel. The blank is translated and rotated relative tothe at least one profiled grinding wheel during the pre-shaping step forgiving the blank approximately a desired profile. However, the Kuehnemethod may be used for external surfaces, and not internal surfaces, andthus is not applicable to the creation of internal slots.

Other methods of producing complex shapes in workpieces are disclosed inU.S. Pat. No. 6,883,234 and U.S. Pat. No. 7,708,619. In U.S. Pat. No.7,708,619 to Subramanian et al., the processes utilizes grinding with alarge diameter wheel operated perpendicular to the surface of the partfor initial formation of a slot within the workpiece. Finishing of theslot to the desired contour is completed using a single-layeredelectroplated tool.

There is a need to develop new methods to form complex shapes withinworkpieces and limit the shortcomings associated with conventionalprocesses.

SUMMARY

According to a first aspect, an abrasive tool includes a bonded abrasivebody having abrasive grains contained within a bonding material, whereinthe bonded abrasive body comprises a complex shape having a form depth(FD) of at least about 0.3, wherein the form depth is described by theequation [(R1−Rs)/R1]. Notably, Rs is a smallest radius (Rs) at a pointalong the longitudinal axis of the bonded abrasive body and R1 is alargest radius (R1) at a point along the longitudinal axis of the bondedabrasive body.

According to another aspect, a method of finishing a workpiece includesrotating a bonded abrasive tool relative to a workpiece for finishing are-entrant shape opening in the workpiece. The bonded abrasive toolincludes a bonded abrasive body having abrasive grains contained withina bonding material, and wherein finishing comprises forming a surfacedefining the re-entrant shape opening having a surface roughness (R_(a))of not greater than about 2 microns.

In yet another aspect, a method of operating an abrasive tool includesfinishing a re-entrant shape opening in a workpiece using a mountedpoint abrasive tool comprising abrasive grains contained within abonding material. The body has a complex shape having a form depth (FD)of at least about 0.3, wherein the form depth is described by theequation [(R1−Rs)/R1], and Rs is a smallest radius (Rs) at a point alongthe longitudinal axis of the body and R1 is a largest radius (R1) at apoint along the longitudinal axis of the body. Notably, Rs is notgreater than about 10 mm. The method further includes plunge dressingthe mounted point abrasive tool along a form length of the body.

Another aspect includes a method of finishing a workpiece includingproviding a workpiece having a re-entrant shaped opening roughly formedin a surface of the workpiece, and finishing the re-entrant shapedopening using a mounted point abrasive tool comprising abrasive grainscontained within a vitreous bond. During finishing, a water-solublecoolant material is provided at an interface of the mounted pointabrasive tool and a surface of the workpiece defining the re-entrantshaped opening.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerousfeatures and advantages made apparent to those skilled in the art byreferencing the accompanying drawings.

FIG. 1 includes a schematic representation of a slot formation process.

FIGS. 2( a) and 2(b) include schematic representations of slots that canbe generated by the slot formation process.

FIG. 3A includes an illustration of a finishing operation using a bondedabrasive tool according to an embodiment.

FIG. 3B includes an illustration of a finished opening in a workpiecehaving a complex shape, wherein the finished opening is formed using abonded abrasive tool according to an embodiment.

FIG. 4 includes a cross-sectional illustration of a bonded abrasive toolhaving a complex shape according to an embodiment.

FIG. 5 includes an illustration of a dressing operation on a bondedabrasive tool having a complex shape according to an embodiment.

FIGS. 6A-6B include plots of performance parameters measured during afinishing operation conducted according to an embodiment.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DETAILED DESCRIPTION

The following is directed to abrasive tools, and more particularlybonded abrasive tools suitable for finishing of surfaces having complexshapes within workpieces. It will be appreciated that bonded abrasivesare a separate and distinct class from other abrasives (e.g. coatedabrasives, etc.) in that bonded abrasives have a three-dimensional shapeincluding a dispersion of abrasive grains throughout out athree-dimensional volume, which are contained within a three-dimensionalvolume of bonding material. Moreover, bonded abrasive bodes may includesome amount of porosity, which may facilitate chip formation andexposure of new abrasive grains Chip formation, abrasive grain exposure,and dressing are certain attributes associated with bonded abrasives,and which distinguish bonded abrasives from other classes of abrasives,such as coated abrasives or single layer electroplated tools.

As used herein, the term “complex shape” refers to a shape (e.g., of anopening within a workpiece) or a shape of a part (e.g., a bondedabrasive body) that has a contour defining a re-entrant shape. Are-entrant shape does not allow a mating form to be removed in adirection normal to one of three axes (i.e., x, y or z). A “re-entrantshape” can be a contour that is re-entering or pointing inward, which iswider at an inner axial position than at an outer axial position (i.e.,an entrance). An example of the re-entrant shape is a dovetail slot, akeystone shape, and the like.

Turbine components, such as jet engine, rotors, compressor bladeassembly, typically employ re-entrant shaped slots in the turbine disks.The re-entrant shape can be used to hold or retain turbine blades aroundthe periphery of turbine disks. Mechanical slides, T-slots to clampparts on a machine table also use such re-entrant shaped slots.

With respect to a process of forming a complex shape in a workpiece, aninitial slot formation process can be undertaken, which forms an openingwithin the workpiece. The opening or slot does not necessarily have thefinal contour (i.e., complex shape). The slot formation process canremove the bulk of material, minimizing the amount of material to beremoved in the complex shape finishing process with a bonded abrasivetool.

FIG. 1 includes an illustration of a slot formation process 10. Asillustrated, the slot formation process can utilize a bonded abrasivetool 12, oriented in a particular manner with respect to the workpiece14, thereby forming slot(s) 16 in workpiece 14. In a particularembodiment, the slot formation processes of the invention can becompleted using a bonded abrasive tool 12 oriented with respect to theworkpiece 14 to conduct a creep-feed grinding process. The creep-feedgrinding can be conducted at grinding speed in a range between about 30m/s and about 150 m/s.

FIGS. 2( a) and 2(b) include schematic representations of slots that canbe generated by the slot formation process. In particular, FIGS. 2( a)and 2(b) include workpieces 18A and 18B that can be formed by the slotformation processes 10 of the invention, respectively. In oneembodiment, slot 16 has a single diameter throughout the depths of theslot 16, as shown in FIG. 2( a). In another embodiment, slot 16 has atleast two distinct diameters at different depths, as shown in FIG. 2(b).

The slot formation process may utilize a particular specific cuttingenergy. For example, the specific cutting energy may be equal to, orless than, about 10 Hp/in³min (about 27 J/mm³), such as between about0.5 Hp/in³ min (about 1.4 J/mm³) and about 10 Hp/in³ min (about 27J/mm³) or between about 1 Hp/in³ min (about 2.7 J/mm³) and about 10Hp/in³ min (about 27 J/mm³).

In another embodiment, the slot formation process can be conducted at aparticular material removal rate (MRR), such as in a range of betweenabout 0.25 in³/min in (about 2.7 mm³/sec/mm) and about 60 in³/min in(about 650 mm³/sec/mm) at a maximum specific cutting energy of about 10Hp/in³min (about 27 J/mm³). Further details of the slot forming process,which may be utilized in conjunction with the finishing processdisclosed herein, are presented in U.S. Pat. No. 7,708,619, theteachings of which are incorporated herein by reference.

The slot formation process, and thus the finishing process of theembodiments herein can be completed on certain types of materials,including hard-to-grind materials. The invention workpieces can bemetallic, and particularly metal alloys such titanium, Inconel (e.g.,IN-718), steel-chrome-nickel alloys (e.g., 100 Cr6), carbon steel (AISI4340 and AISI 1018) and combinations thereof. In accordance with oneembodiment, the workpiece can have hardness value of equal to or lessthan about 65 Rc, such as between about 4 Rc and about 65 Rc (or 84 to111 Rb hardness). This is in contrast to prior art machining processesthat typically can be used only for softer materials, i.e., those havinga maximum hardness value of about 32 Rc. In one embodiment, the metallicworkpieces for the invention have a hardness value of between about 32Rc and about 65 Rc or between about 36 Rc and about 65 Rc.

In the slot formation process, a bonded abrasive tool can be used, suchas grinding wheels and cutoff wheels. The bonded abrasive tool for usein the slot formation process can include at least about 3 volume % (ona tool volume basis) of a filamentary sol gel alpha-alumina abrasivegrain, optionally including secondary abrasive grains or agglomeratesthereof. Suitable methods for making bonded abrasive tools are disclosedin U.S. Pat. Nos. 5,129,919; 5,738,696; 5,738,697; 6,074,278; and6,679,758 B, and U.S. patent application Ser. No. 11/240,809 filed Sep.28, 2005, the teachings of which are incorporated herein by reference.Particular details of the bonded abrasive tool used in the slot formingprocess are provided in U.S. Pat. No. 7,708,619, the teachings of whichare incorporated herein by reference.

Referring now to operations following the slot formation process, afinishing process can be conducted to change the contour of the slot toa complex shape (e.g., re-entrant shape). The tools used to conduct theslot formation and the finishing process can be part of high efficiencygrinding machines, including multi-axis machining centers. With amulti-axis machining center, both the slot formation and the complexshape finishing process can be carried out on the same machine. Suitablegrinding machines include, e.g., a Campbell 950H horizontal axisgrinding machine tool, available from Campbell Grinding Company, SpringLake, Mich., and a Blohm Mont. 408, three axis, CNC creep feed grindingmachine, available from Blohm Maschinenbau GmbH, Germany.

FIG. 3A includes an illustration of a finishing operation using a bondedabrasive tool according to an embodiment. In particular, FIG. 3Aillustrates a finishing operation to form a complex shape within theslot 16 of the workpiece 14 with a bonded abrasive tool 301 in the formof a mounted point tool. The bonded abrasive tool 301 can have a complexshape suitable for producing a corresponding complex shape within theworkpiece 14. That is, the bonded abrasive body 303 can have a shapethat is the inverse of a complex shape, to be imparted into theworkpiece 14.

In accordance with embodiments herein, the bonded abrasive tool 301 canhave a bonded abrasive body 303 including abrasive grains containedwithin a matrix of bonding material. That is, the bonded abrasive toolincorporates abrasive grains dispersed throughout a three-dimensionalmatrix of bonding material. In accordance with an embodiment, theabrasive grains can include superabrasive materials. For example,suitable superabrasive materials can include cubic boron nitride,diamond, and a combination thereof. In certain instances, the bondedabrasive body 303 can include abrasive grains that consist essentiallyof diamond. However, in other tools, the bonded abrasive body 303 caninclude abrasive grains that consist essentially of cubic boron nitride.

The bonded abrasive tool can be formed such that it has an abrasive bodyincorporating abrasive grains having an average grit size of not greaterthan about 150 microns. In some embodiments, the abrasive grains canhave an average grit size of not greater than about 125 microns, such asnot greater than about 100 microns, or even not greater than about 95microns. In particular instances, the abrasive grains have an averagegrit size within a range between about 10 microns and 150 microns, suchas between about 20 microns and 120 microns, or even between about 20microns and 100 microns.

With regard to the bonding material within the bonded abrasive body 303,suitable materials can include organic materials, inorganic materials,and a combination thereof. For example, suitable organic materials mayinclude polymers such as resins, epoxies, and the like.

Some suitable inorganic bond materials can include metals, metal alloys,ceramic materials, and a combination thereof. For example, some suitablemetals can include transition metal elements and metal alloys containingtransition metal elements. In other embodiments, the bond material maybe a ceramic material, which can include polycrystalline and/or vitreousmaterials. Suitable ceramic bonding materials can include oxides,including for example, SiO₂, Al₂O₃, B₂O₃, MgO, CaO, Li₂O, K₂O, Na₂O andthe like.

Further, it will be appreciated that the bonding material can be ahybrid material. For example, the bonding material can include acombination of organic and inorganic components. Some suitable hybridbond materials can include metal and organic bond materials.

In accordance with at least one embodiment, the bonded abrasive tool 301can include a composite including bond material, abrasive grains, andsome porosity. For example, the bonded abrasive tool 301 can have atleast about 3 vol % abrasive grains (e.g., superabrasive grains) of thetotal volume of the bonded abrasive body. In other instances, the bondedabrasive tool 301 can include at least about 6 vol %, at least about 10vol %, at least about 15 vol %, at least about 20 vol %, or even atleast about 25 vol % abrasive grains. Particular bonded abrasive tools301 can be formed to include between about 2 vol % and about 60 vol %,such as between about 4 vol % and about 60 vol %, or even between about6 vol % and about 54 vol % superabrasive grains.

The bonded abrasive tool 301 can be formed to have at least about 3 vol% bond material (e.g., vitrified bond or metal bond material) of thetotal volume of the bonded abrasive body. In other instances, the bondedabrasive tool 301 can include at least about 6 vol %, at least about 10vol %, at least about 15 vol %, at least about 20 vol %, or even atleast about 25 vol % bond material. Particular bonded abrasive tools 301can include between about 2 vol % and about 60 vol %, such as betweenabout 4 vol % and about 60 vol %, or even between about 6 vol % andabout 54 vol % bond material.

The bonded abrasive tool 301 can be formed to have a certain content ofporosity, and particularly an amount of not greater than about 60 vol %of the total volume of the bonded abrasive body. For example, the bondedabrasive body 301 can have not greater than about 55 vol %, such as notgreater than about 50 vol %, not greater than about 45 vol %, notgreater than about 40 vol %, not greater than about 35 vol %, or evennot greater than about 30 vol % porosity. Particular bonded abrasivetools 301 can have a certain content of porosity, such as between about0.5 vol % and about 60 vol %, such as between about 1 vol % and about 60vol %, between about 1 vol % and about 54 vol %, between about 2 vol %and about 50 vol %, between about 2 vol % and about 40 vol %, or evenbetween about 2 vol % and about 30 vol % porosity.

During the finishing process, a bonded abrasive tool 301 can be placedin contact with the workpiece 14, and more particularly within the slot16 previously formed within the workpiece 14. In accordance with anembodiment, the bonded abrasive tool 301 can be rotated at asignificantly high speed to finish and recontour the surfaces 321 and323 of the slot 16 to form a complex shape within the workpiece 14 (seefor example 351 of FIG. 3B). For example, the bonded abrasive tool canbe rotated at speeds of at least about 10,000 rpm. In other instances,the tool may be rotated at greater speeds, such as at least about 20,000rpm, at least about 30,000 rpm, at least about 40,000 rpm, or evengreater. Still, in certain instances the bonded abrasive tool 301 isrotated relative to the workpiece 14 at a speed within a range betweenabout 10,000 and 250,000 rpm, such as between about 10,000 rpm and125,000 rpm, about 10,000 rpm and 110,000 rpm, or even between about10,000 rpm and about 100,000 rpm.

During finishing, the bonded abrasive tool 301 can be moved along anaxis relative to the workpiece 14 to facilitate finishing of the surface321 to a suitable, complex shape. For example, in certain instances thebonded abrasive tool 301 can follow a reciprocating pathway or completea box cycle. For example, in a first pass of the reciprocating pathway,the bonded abrasive tool 300 can be moved relative to the workpiece 14along a path 308. Movement of the bonded abrasive tool 300 along thepath 308 facilitates finishing of the full thickness of the surface 321.According to one type of reciprocating pathway, after completing thefirst pass along path 308, the bonded abrasive tool 301 can be shiftedlaterally along the axis 375 and moved along a path 309 in a secondpass. According to this particular reciprocating pathway, during thesecond pass, the surface of the bonded abrasive tool 301 can contactsurface 323 of the slot 16 opposite the surface 321, thereby finishingthe portion of the slot 16 defined by the surface 323. After the bondedabrasive tool 301 travels along the full thickness of the workpiecethrough the slot 16, the tool can then again be shifted laterally alongthe axis 375 and returned to the path 308 for another (i.e., third) passalong the surface 321. It will be appreciated that the bonded abrasivetool 301 may be reciprocated and moved along paths 308 and 309 for adesignated number of turns until the surfaces 321 and 323 aresatisfactorily finished. It will further be appreciated that while thepaths 308 and 309 are illustrated as being linear, certain processes canutilize paths that are curved or utilize an arced direction.

According to an alternative embodiment, the reciprocating pathway can beconducted such that one surface of the slot is finished before anothersurface is finished. For example, the bonded abrasive tool 301 can bemoved along a first surface 321 for multiple, sequential passes (i.e.,back and forth along path 308) until the first surface 321 is finishedwith a suitable complex shape. After finishing the first surface 321,the bonded abrasive tool can be shifted laterally along the axis 375 tocontact the second surface 323 of the slot 16 opposite the first surface323. The bonded abrasive tool 301 can then again be moved along thethickness of the slot 16 (i.e., back and forth along the path 309) alongthe second surface 323 for multiple, sequential passes until the secondsurface 323 is finished.

In accordance with one embodiment, the finishing process may remove aparticular amount of material from the surface of the slot on each pass.For example, during finishing, the bonded abrasive tool 301 may removematerial from the surface 321 to a depth of not greater than 100 micronsfor each pass of the bonded abrasive tool 301 through the slot 16. Inother embodiments, the finishing operation may be conducted such thatthe material is removed to a depth of not greater than about 75 microns,such as not greater than about 65 microns, such as not greater thanabout 50 microns, or even less for each pass of the bonded abrasive tool301 through the slot 16. In particular instances, each pass of thebonded abrasive tool 301 may remove material to a depth within a rangebetween 1 micron and about 100 microns, such as between about 1 micronand about 75 microns, or even between about 10 microns and about 65microns.

Moreover, during finishing, the feed rate of the bonded abrasive tool,which is a measure of the lateral movement of the bonded abrasive toolalong the axis 375 between sequential passes at the same surface can beat least about 30 ipm [762 mm/min]. In other embodiments, the feed ratecan be greater, such as at least about 50 ipm [1270 mm/min], at leastabout 75 ipm [1905 mm/min], at least about 100 ipm [2540 mm/min], oreven at least about 125 ipm [3175 mm/min]. Certain finishing processesutilize a feed rate within a range between about 30 ipm [762 mm/min] andabout 300 ipm [7620 mm/min], such as between about 50 ipm [1270 mm/min]and about 250 ipm [6350 mm/min], or even within a range between about 50ipm [1270 mm/min] and about 200 ipm [5080 mm/min].

The finishing operation to form the re-entrant shape in the workpiecemay be conducted at specific material removal rates. For example, thematerial removal rate during the finishing operation can be at leastabout 0.01 inches³/min/inch [0.11 mm³/sec/mm]. In other instances, thefinishing process can be conducted at a material removal rate of atleast about 0.05 inches³/min/inch [0.54 mm³/sec/mm], such as at leastabout 0.08 inches³/min/inch [0.86 mm³/sec/mm], at least about 0.1inches³/min/inch [1.1 mm³/sec/mm], at least about 0.3 inches³/min/inch[3.2 mm³/sec/mm], at least about 1 inch³/min/inch [11 mm³/sec/mm], atleast about 1.5 inches³/min/inch [16 mm³/sec/mm], or even at least about2 inches³/min/inch [22 mm³/sec/mm].

For certain finishing operations, the material removal rate can be notgreater than about 1.5 inches³/min/inch [16 mm³/sec/mm]. Still, certainfinishing processes may have a material removal rate of not greater thanabout 1 inch³/min/inch [11 mm³/sec/mm], not greater than about 0.8inches³/min/inch [8.6 mm³/sec/mm], or even not greater than about 0.3inches³/min/inch [3.2 mm³/sec/mm].

In particular instances, the finishing process can be conducted suchthat the material removal rate can be within a range between about 0.01inches³/min/inch [0.11 mm³/sec/mm]and about 2 inches³/min/inch [22mm³/sec/mm], such as between about 0.03 inches³/min/inch [0.32mm³/sec/mm] and about 1.5 inches³/min/inch [16 mm³/sec/mm].

The finishing operation in accordance with embodiments herein mayfurther be conducted at a specific finishing power. For example, thefinishing power used during the finishing operation can be not greaterthan about 5 Hp [3.75 kW] at a feed rate of the mounted point toolwithin a range between about 30 ipm [762 mm/min] and about 300 ipm [7620mm/min]. According to certain other embodiments, during finishing thefinishing power can be not greater than about 4 Hp [3.0 kW], such as notgreater than about 3.8 Hp [2.83 kW], not greater than about 3.6 Hp [2.68kW], not greater than about 3.4 Hp [2.54 kW], not greater than about 3.2Hp [2.39 kW], or even not greater than about 3 Hp [2.25 kW]. Suchfinishing powers may be used at a feed rate of the within a rangebetween about 30 ipm [762 mm/min] and about 300 ipm [7620 mm/min].

It will also be appreciated that the finishing operation is distinctfrom other material removal operations in that the surface of theworkpiece upon completion of the finishing operation can have particularcharacteristics. For example, turning to FIG. 3B, a cross-sectionalillustration of a portion of a workpiece having a finishedreentrant-shaped opening 351 is illustrated in accordance with anembodiment. As illustrated, the workpiece 14 can have a re-entrantshaped opening 351 formed therein and defined by surfaces 326 and 327which have substantially similar contours to that of the bonded abrasivetool 301. In accordance with an embodiment, the finishing processincludes forming a surface 326 having has a surface roughness (R_(a)) ofnot greater than about 2 microns. In other instances, the surfaceroughness (R_(a)) may be less, such as not greater than about 1.8microns, such as not greater than about 1.5 microns. In particularinstances, the surface roughness (R_(a)) can be within a range betweenabout 0.1 microns and about 2 microns. The surface roughness of thefinished surfaces can be measured using a Profilometer, such as aMarSurf UD 120/LD 120 model Profilometer, commonly available fromMahr-Federal Corporation, and operated using MarSurf XCR software.

Upon completion of the finishing operation, the surfaces 326 and 327defining the re-entrant shaped opening 351 are essentially free of burn.Burn may be evidence as portions of the surfaces 326 or 327 beingdiscolored or having a residue or after etching having a whitishappearance indicating thermal damage to the surfaces during thefinishing operation. Finishing processes conducted according to theembodiments herein are capable of producing final surfaces exhibitinglittle to no burn.

Finishing operations conducted in accordance with embodiments herein mayutilize a coolant provided at the interface of the bonded abrasive tool301 and surface 321 or 323 of the slot 16. The coolant may be providedin a coherent jet as described in U.S. Pat. No. 6,669,118. In otherembodiments, the coolant may be provided by flooding the interface area.The bonded abrasive bodies of the embodiments herein may facilitate useof a water-soluble coolant, which may be preferable for environmentalreasons over certain other coolants (e.g. non water-soluble coolants).Other suitable coolants can include use of semi-synthetic and/orsynthetic coolants. Still, it will be appreciated, that for certainoperations, oil-based coolants can be used.

FIG. 4 includes a cross-sectional illustration of an abrasive tool inaccordance with an embodiment. In particular, the abrasive tool can be amounted point abrasive tool which is configured to be rotated at highspeeds for finishing of surfaces as described herein. Notable, theabrasive tool includes a bonded abrasive body incorporating abrasivegrains dispersed throughout a volume and contained within a volume ofbonding material as described herein. More particularly, as illustratedin FIG. 4, the bonded abrasive body can have a complex shape configuredto finish complex shapes within a workpiece (e.g. re-entrant shapes).

In accordance with one embodiment, the bonded abrasive body 401 can havea longitudinal axis 450 extending along the length of the body 401(i.e., the longest dimension of the body) between an upper surface 404and a lower surface 403. Additionally, a lateral axis 451 can extendperpendicular to the longitudinal axis 450 and define the width of thebody 401. In accordance with one embodiment, the complex shape of thebonded abrasive body 401 can be defined by a first radial flange 410extending from the bonded abrasive body at a first axial position. Forexample, the first radial flange 410 can extend laterally along thelateral axis 451 and circumferentially around the body 401. The flange410 can have a first surface 411 that extends radially from the body 401at a first angle relative to the lateral axis 451. As illustrated, theintersection of the first surface 411 and the lateral axis 451 candefine an acute angle 461. Likewise, the flange 410 can be furtherdefined by a second surface 412 extending radially from the bondedabrasive body 410. The second surface 412 can be adjacent to, and evenabutting, the first surface 411. The surface 412 can define an acuteangle 462 between the lateral axis 451 and the surface 412.

Additionally, the bonded abrasive body 401 may be formed such that itincludes a second radial flange 413, which may be distinct from thefirst radial flange 410. In fact, as illustrated in FIG. 4, the radialflange 413 can be spaced apart from the radial flange 410 along thelongitudinal axis 450 at a second axial position, distinct from theaxial position of the radial flange 410. In accordance with anembodiment, the radial flange 413 can be defined by surfaces 414 and 415that can extend radially and circumferentially from the bonded abrasivebody to define the flange 413.

In some instances, the cross-sectional shape of the bonded abrasive body401 may be described as a single-flanged shape, double-flanged shape,triple-flanged shape, and the like. Such shapes can incorporate one ormore radial flanges extending from the body to define a re-entrantshape. In other instances, it may be described as a re-entrant-shapedbody such that is has dimensions suitable for finishing and forming of are-entrant shape into a workpiece.

In accordance with one embodiment, the complex shape of the bondedabrasive body 401 may be described by a form depth (FD). The form depthcan be described by the equation [(R1−Rs)/R1], wherein Rs is a smallestradius (Rs) (i.e., half of the dimension 406) of the bonded abrasivebody 401 at a point along the longitudinal axis 450 and R1 is a largestradius (R1) (i.e., half of the dimension 408) of the bonded abrasivebody 401 at a point along the longitudinal axis 450.

In one embodiment, the bonded abrasive body 401 has a form depth (FD) ofat least about 0.3. In other embodiments, the bonded abrasive body 401can have a form depth (FD) of at least about 0.4, at least about 0.5, atleast about 0.6, at least about 0.7, or greater. Certain embodiments mayutilize a bonded abrasive body 401 having a form depth (FD) within arange between about 0.3 and about 0.95, such as between about 0.4 andabout 0.9, such as between about 0.5 and about 0.9.

The bonded abrasive body 401 may also be described by a form ratio (FR)described by the equation [F1/Fw]. The dimension F1 is a form lengthmeasured as a dimension of the peripheral profile surface along adirection of the longitudinal axis 450 of the bonded abrasive body 401.In particular, the form length can describe the profile length of thebonded abrasive body 401 between points A and B illustrated on FIG. 4,defining the portion of the profile actively engaged in the materialremoval finishing process. The dimension Fw is a form width, whichactually defines the length of the bonded abrasive body between the topsurface 404 and the bottom surface 403 along a straight line of thelongitudinal axis 450.

In accordance with one embodiment, the bonded abrasive body 401 can havea form ratio [F1/Fw] of at least about 1.1. In other instances, thebonded abrasive body 401 can have a form ratio of at least about 1.2,such as at least about 1.3, at least about 1.4, at least about 1.5, oreven at least about 1.7. Particular embodiments may utilize a bondedabrasive body having a form ratio within a range between about 1.1 andabout 3.0, such as between about 1.2 and about 2.8, such as betweenabout 1.2 and about 2.5, such as between about 1.3 and about 2.2, oreven between about 1.3 and about 2.0.

Certain dimensional aspects of the bonded abrasive body 401 may furtherbe described by an overhang ratio. The overhang ratio of the bondedabrasive body 401 can be described by the equation [OL/Dm], wherein Dmis a minimum diameter 406 at a point along the longitudinal axis 450 ofthe bonded abrasive body and OL is the length 407 between the bottomsurface 403 of the bonded abrasive body 401 and the point along thelongitudinal axis of the bonded abrasive body defining the minimumdiameter 406.

According to certain embodiments, the bonded abrasive body 401 can havean overhang ratio (OR) of at least about 1.3. In still other instances,the bonded abrasive body 401 may be formed such that it has an overhangratio of at least about 1.4, such as at least about 1.5, or even atleast about 1.6. The overhang ratio for bonded abrasive body 401 can bewithin a range between about 1.3 and about 2.5, such as between about1.3 and about 2.2.

In addition to the characteristics described herein, the bonded abrasivetools can be dressed in-situ with the finishing process. Dressing isunderstood in the art as a method of sharpening and reshaping of abonded abrasive body, and is typically an operation conducted on bondedabrasive articles and not an operation suitable for use with otherabrasive articles, including for example, single-layered abrasive tools(e.g. electroplated abrasive bodies).

FIG. 5 includes a cross-sectional illustration of a dressing operationin accordance with an embodiment. In particular, FIG. 5 includes across-sectional view of a portion of a bonded abrasive tool 400including a bonded abrasive body having abrasive grains contained withina matrix of bond material. The bonded abrasive tool according toembodiments herein can be dressed during finishing operations tomaintain the contour of the bonded abrasive body, which facilitatesimproved accuracy of the finishing operation and improved tool life overother conventional mounted point abrasive tools.

During a dressing operation, a dressing material 501, which may includea significantly sharp material, can be placed in contact with theprofile edge of the bonded abrasive body 401. The bonded abrasive body401 may be rotated relative to the dressing material 501 to sharpen andrecontour the profile edge of the bonded abrasive body. Alternatively,during dressing the dressing material 501 may be rotated relative to thebonded abrasive body 401. Or in another alternative embodiment, thebonded abrasive body 401 and dressing material 501 can be rotated at thesame time, and may be rotated in the same direction or in oppositedirections depending upon the type of dressing.

In particular, FIG. 5 illustrates a plunge dressing operation, whereinthe dressing material 501 is placed in full contact with the form lengthof the abrasive body 401. Plunge dressing may offer a significantadvantage over other operations as a mechanism to keep the bondedabrasive body 401 having a particular contour suitable for finishing ofthe surfaces of the workpiece to a complex shape and tight dimensionaltolerances. Notably, to conduct a plunge dressing operation, the surfaceof the dressing material 501 has significantly the same complex contouras the form length of the abrasive body 401 for proper recontouring ofthe abrasive body 401. That is, the dressing material 501 can be shapedto have a complementary complex shape, such that the dressing material501 can engage the bonded abrasive body 401 along the full periphery ofthe form length during dressing. The ability to dress the bondedabrasive body 401 during the finishing operation can facilitate longertool life and improved consistency of the finish surfaces includingdimensions and surface geometries (e.g. R_(a)).

While FIG. 5 illustrates a plunge dressing operation, other dressingoperations, including for example, a traverse dressing operation, can beutilized with the bonded abrasive articles of the present embodiments.Traverse dressing can include placing a dressing material in contactwith the bonded abrasive, particularly in contact with a portion of theprofile of the bonded abrasive body. Notably, traverse dressing differsfrom plunge dressing in that only a portion of the form length isdressed at any time, since the dressing material is not necessarilygiven a complex shape to complement the complex shape of the bondedabrasive body, as is the case in plunge dressing. Rather, traversedressing operations utilize a dressing material that is moved, ortraversed, along the complex shape of the form length of the bondedabrasive body until the full form length has been dressed. Traversedressing may be completed in situ with finishing operations.

EXAMPLES

A workpiece of Inconel 718 having dimensions of 2.85×2.00×1.50 incheswas placed in a modified Cinternal ID/OD two-axis CNC grinder availablefrom Heald Grinders.

A finishing operation was conducted on the workpiece using a vitrifiedCBN mounted point tool (B 120-2-B5-VCF10) from Saint-Gobain Corporationhaving a complex shape as illustrated in FIG. 4. The bonded abrasivebody had a form depth (FD) of 0.8, a form ratio (FR) of 1.5, and anoverhang ratio of 1.57. The tool had a form width of approximately 4.1cm, an overhang length (OL) of 1.19 cm, a minimum diameter of 0.762 cm,and a maximum diameter of 3.76 cm.

The finishing process was conducted to simulate finishing of one 2 inchthick rotor with 60 slots to completion (equivalent to removing 1.2inches of material from a 2 inch workpiece). During finishing, the depthof cut per pass was 0.0005″, such that the total depth of cut was a0.010 inch on each side of a slot at a wheel speed of 40,000 rpm.Notably, the wheel speed of 40,000 rpm produced a range of surfacespeeds on the bonded abrasive tool ranging from a maximum at the largestdiameter of 16,755 sfpm to 3,140 sfpm at the smallest diameter. Twofinishing operations were conducted at work speeds of 50 ipm and 100ipm, and for each of the work speeds, two separate workpieces were used.For each of the tests, 1.2 inches of material was removed from theworkpieces without dressing.

On the first test workpiece, 40 passes or 0.020″ depth of material wasremoved from an end of the workpiece (equivalent to completing oneslot). On the second workpiece, 0.400 inches of material was removedfrom each end. Finally, the first workpiece was again used, and 0.400inches of material was removed from a second end. After finishing, theworkpieces were sent for analysis of wear to the finished surfaces.Based on the analysis, there was limited evidence of burn (i.e., whitelayer of material on the surfaces) and evidence that the finishedsurfaces were within commercial specifications.

During finishing, an oil coolant (Master Chemical OM-300) was providedat the interface of the bonded abrasive tool and the surface of theworkpiece using a nozzle designed to target multiple jets across theform at 100 psi with a flow rate of approximately 29.2 gpm.

The bonded abrasive body was dressed under the conditions set forth inTable 1 below. The bonded abrasive body was dressed twice; once at thestart of the 100 ipm test and again at the start of the 50 ipm test.

TABLE 1 Dressing Conditions Mounted Point Speed (rpm): 40,000 Dress RollSpeed (rpm): 3,650 Feed per Mounted point revolution (μin): 3.75 Feedrate (ipm): 0.15 Speed Ratio Range (max/min): 1.83-.27

Certain performance parameters are illustrated in the plots of FIGS. 6Aand 6B. FIG. 6A includes a plot of finishing power (Hp) versus slotlength (i.e., the number of inches of slot length finished) for thefinishing operations. In particular, plot 601 represents power versusslot length for the finishing operation conducted at 50 ipm and plot 603represents power versus slot length for the finishing operation 100 ipm.As noted, the finishing power did not exceed 2.2 Hp for the materialremoval process at 50 ipm, and the finishing power did not exceed 2.8 Hpfor material removal at 100 ipm. The results demonstrate significantlylimited finishing power necessary for many slots.

FIG. 6B includes plots of finishing power (Hp) versus specific materialremoval rate corresponding to 50 and 100 ipm for various lengths ofcompleted slot. As demonstrated by FIG. 6B, the finishing power was lessthan 2.8 Hp for specific material removal rates of up to 0.5 in³/min/in.The results demonstrate significantly limited power necessary forfinishing of the surface with commercially acceptable material removalrates.

The abrasive tool and method of finishing workpieces using the abrasivetools of embodiments herein represent a departure from the state of theart. In particular, state of the art mechanisms for finishing suchworkpieces and materials, particularly to form re-entrant shapes inmaterials to tight dimensional tolerances have not utilized the tools ormechanisms described herein. In particular, the abrasive tools ofembodiments herein utilize a combination of features including, forexample, abrasive grains disbursed volumetrically in a matrix of bondingmaterial, complex shapes described by form depth, overhang ratio, andform ratio. Moreover, the bonded abrasive tools of embodiments hereinare utilized in a particular manner to facilitate finishing operationshaving characteristics which have not been utilized before. Inparticular, the bonded abrasive tools are capable of finishingworkpieces to complex re-entrant shapes under particular conditionsincluding locational speeds of the tool, feed rates, material removalrates, finishing power, and the like. Moreover, utilization of theabrasive tools herein in combination with the methods describedfacilitates a new process for finishing of workpieces to tightdimensional tolerances while maintaining the shape of the tool therebyfacilitating accuracy of the shape and surface formed and extending theusable life of the tool thereby improving the efficiency of theoperation.

What is claimed is:
 1. An abrasive tool comprising: a bonded abrasivebody having abrasive grains dispersed throughout a three-dimensionalvolume of a bonding material, wherein the bonded abrasive body comprisesa complex shape having a form depth (FD) of at least about 0.3, whereinthe complex shape comprises a first radial flange extending from thebonded abrasive body at a first axial position.
 2. The abrasive tool ofclaim 1, wherein the first radial flange comprises a first surfaceextending radially from the bonded abrasive body at a first anglerelative to a lateral axis of the bonded abrasive body.
 3. The abrasivetool of claim 2, wherein the first angle is an acute angle.
 4. Theabrasive tool of claim 1, wherein the complex shape comprises a secondradial flange extending from the bonded abrasive body at a second axialposition, wherein the first radial flange and second radial flange arespaced apart from each other along a longitudinal axis of the bondedabrasive body.
 5. The abrasive tool of claim 1, wherein the bondedabrasive body comprises a form ratio (FR) of at least about 1.1.
 6. Theabrasive tool of claim 1, wherein the complex shape comprises a radialchannel extending between first and second radial flanges extendingaxially from the bonded abrasive body.
 7. The abrasive tool of claim 1,wherein the bonding material comprises a vitreous bonding material andwherein the vitreous bonding material comprises between about 2 vol %and about 60 vol % of the total volume of the bonded abrasive body. 8.The abrasive tool of claim 1, wherein the form depth (FD) is within arange between about 0.3 and about 0.95.
 9. The abrasive tool of claim 1,wherein the abrasive grains have an average grit size of between about20 microns and 100 microns.
 10. The abrasive tool of claim 1, whereinthe abrasive grains comprise between about 6 vol % and about 54 vol % ofthe total volume of the bonded abrasive body.
 11. The abrasive tool ofclaim 1, wherein the body comprises an amount of porosity within a rangebetween about 2 vol % and about 30 vol % of the total volume of thebonded abrasive body.
 12. The abrasive tool of claim 1, wherein thefirst radial flange comprises a second surface adjacent the firstsurface and extending radially from the bonded abrasive body at a secondangle relative to a lateral axis of the bonded abrasive body.
 13. Theabrasive tool of claim 12, wherein the second angle is an acute angle.14. A method of operating an abrasive tool comprising: finishing are-entrant shape opening in a workpiece using a mounted point abrasivetool comprising a bonded abrasive body comprising abrasive grainsdispersed throughout a three-dimensional volume of a bonding material,wherein the bonded abrasive body comprises a complex shape having a formdepth (FD) of at least about 0.3; and plunge dressing the mounted pointabrasive tool along a form length of the bonded abrasive body.
 15. Themethod of claim 14, wherein dressing comprises rotating a dressing bodyat different velocities at different positions along a form length ofthe bonded abrasive body.
 16. The method of claim 14, wherein finishingcomprises forming a finished surface defining the re-entrant shapeopening in the workpiece having an average surface roughness (R_(a)) ofnot greater than about 2 microns.
 17. The method of claim 14, whereinduring finishing a water-soluble coolant material is provided at aninterface of the mounted point abrasive tool and a surface of theworkpiece defining the re-entrant shaped opening.
 18. The method ofclaim 14, wherein during finishing, the material removal rate is withina range between about 0.03 inches³/min/inch [0.32 mm³/sec/mm] and about1.5 inches³/min/inch [16 mm³/sec/mm].
 19. The method of claim 14,wherein during finishing, the finishing power used is not greater thanabout 3 Hp [2.25 kW] at a feed rate of the mounted point tool within arange between about 30 ipm [762 mm/min] and about 300 ipm [7620 mm/min].20. The method of claim 14, wherein after finishing, the workpiece isessentially free of burn.